Electronic systems often have an evaluation unit for providing measuring signals to be processed in the system. Typically, the evaluation unit is part of a control and regulation system and connected to a sensor unit, which is disposed at a distance from the system, via one or a plurality of connection lines. Under rough operating conditions as they may occur in a motor vehicle, for example, the connection line between the evaluation unit and the sensor unit can be interrupted or short-circuited with other connection lines. This could lead to a malfunction of the system without the fault being detected if the measured variable supplied by the sensor unit is plausible.
The safety during operation of the system having the evaluation unit and the external sensor unit is able to be increased by performing a diagnosis of the connection line with regard to the aforementioned faults. To this end, a voltage measured on the connection line is usually subjected to a plausibility check. To determine a line break on the sensor supply, i.e., on the corresponding connection lines carrying the supply voltage, the voltage drop, for instance, is monitored via a measuring resistor (shunt) lying in the connection line. In a correct connection, the supply current of the sensor unit causes a voltage drop, which is able to be measured. If the voltage drop is missing, then an interrupted line can be assumed. If the voltage is too high downstream from the resistor, provided the sensor unit has a lower supply voltage than the evaluation unit of the overall system, then this indicates a short circuit downstream from the voltage supply of the evaluation unit. If the measured voltage is too low, then a short circuit to a ground potential is present. With the aid of a corresponding wiring configuration with resistors, the voltage range of the output of the sensor unit is limited to values greater than 0 V (ground potential) and smaller than the supply voltage of the sensor unit, in order to be able to distinguish the normal operation from short circuits to ground and the supply voltage of the sensor unit or the evaluation unit.
Due to tolerances of the supply current of the sensor unit and tolerances of the resistor of the supply lines and the sensor unit over the service life and temperature, a marked voltage drop results at the measuring resistor, which could lead to high power losses in the measuring resistor in the supply line, so that large components, which can accommodate a correspondingly high output, must be employed. Furthermore, a measuring resistor and a corresponding measuring channel for each connection line to be diagnosed are required in the evaluation unit. This typically entails extra work and expense, and the overall device requires considerable space.
It is the object of this invention to provide a sensor system having an evaluation unit and an external sensor unit, which has a simple configuration and is able to detect interruptions of connection lines in a reliable manner and with a minimum of circuit expenditure.
This object is achieved by the sensor system as described herein.
Further advantageous refinements of the present invention are specified herein.